(a) Field of the Invention
The invention relates to an apparatus and method for manufacturing molten iron. More particularly, the invention relates to an apparatus and method for manufacturing molten iron in which fine direct reduced iron and calcined additives are supplied to a melter-gasifier after these materials undergo hot compacting to thereby manufacture molten iron.
(b) Description of the Related Art
The iron and steel industry is a core industry that supplies the basic materials needed in construction and in the manufacture of automobiles, ships, home appliances, and many of the other products we use. It is also an industry with one of the longest histories that has progressed together with humanity. In an iron foundry, which plays a pivotal roll in the iron and steel industry, after molten iron (i.e., pig iron in a molten state) is produced using iron ore and coal as raw materials, steel is produced from the molten iron then supplied to customers.
Approximately 60% of the world's iron production is realized using the blast furnace method developed in the 14th century. In the blast furnace method, coke produced using as raw materials iron ore and bituminous coal that have undergone a sintering process are placed in a blast furnace, and oxygen is supplied to the furnace to reduce the iron ore to iron to thereby manufacture molten iron. The blast furnace method, which is a main aspect of molten iron production, requires raw materials having a hardness of at least a predetermined level and grain size that can ensure ventilation in the furnace. As a carbon source used as fuel and a reducing agent, specific raw coal depends on coke that has undergone processing, and as an iron source, there is a dependence primarily on sintered ore that has undergone a successive compacting process. Accordingly, in the modern blast furnace method, it is necessary to include raw material preparation processing equipment such as coke manufacturing equipment and sintering equipment, and not only is it necessary to obtain accessory equipment in addition to the blast furnace, but equipment to prevent and minimize the generation of pollution in the accessory equipment is needed. The amount of investment, therefore, is considerable, ultimately increasing manufacturing costs.
In order to solve these problems of the blast furnace method, significant effort is being put forth in iron foundries all over the world to develop a smelting reduction process that produces molten iron by directly using common coal as fuel and a reducing agent, and also directly using fine ores, which make up over 80% of the world's ore production, as an iron source.
U.S. Pat. No. 5,534,046 discloses an apparatus for manufacturing molten iron that directly uses common coal and fine ores. FIG. 9 shows a simplified version of an apparatus for manufacturing molten iron disclosed in U.S. Pat. No. 5,534,046. As shown in FIG. 9, a conventional molten iron manufacturing apparatus 900 includes three fluidized-bed reactors 910 in which fluidized beds are formed, and a melter-gasifier 960 connected thereto. Fine ores and additives at room temperature are charged in the first fluidized-bed reactor, then sequentially passed through all three of the fluidized-bed reactors 910. Since high temperature reducing gas is supplied to the three fluidized-bed reactors 910 from the melter-gasifier 960, the fine ores and additives increase in temperature as a result of the contact made with the high temperature reducing gas. At the same time, 90% or more of the fine ores and additives at room temperature is reduced, and 30% or more of the same is calcined then charged into the melter-gasifier 960.
Coal is supplied to the melter-gasifier 960 to form a coal packed bed, and the fine ores and additives at room temperature undergo fusion and slagging in the coal packed bed to be exhausted as molten iron and slag. Oxygen is supplied through a plurality of tuyeres mounted to an outer wall of the melter-gasifier 960 such that the coal packed bed is burned and converted into high temperature reducing gas, after which the high temperature reducing gas is supplied to the fluidized-bed reactors 910. Following reduction of the fine ores and additives at room temperature, they are exhausted outside.
However, in the molten iron manufacturing apparatus 900 described above, a high speed gas stream is formed to an upper end of the melter-gasifier 960 such that the fine direct reduced iron and the calcined additives charged in the melter-gasifier 960 undergo scattering loss. Furthermore, in the case where the fine direct reduced iron and the calcined additives are charged in the melter-gasifier 960, it is difficult to ensure that the coal packed bed in the melter-gasifier 960 is able to be ventilated and can flow freely.
To overcome this problem, there is being researched a method in which fine direct reduced iron and calcined additives are hot compacted and charged in a melter-gasifier. As an example, a method and apparatus for manufacturing elliptical sponge iron briquettes are disclosed in U.S. Pat. No. 5,666,638. Also, U.S. Pat. Nos. 4,093,455, 4,076,520, and 4,033,559 disclose a method and apparatus for manufacturing plate-shaped and corrugated irregular sponge briquettes. Such sponge briquettes are realized by hot compacting fine direct reduced iron then cooling the same to obtain a density of 5 tons/m3 such that the sponge briquettes are suitable for long distance transportation.
However, if compacted material with a high density as described above is charged into a melter-gasifier, a melting point of reduced iron that is melted in the coal packed bed in the melter-gasifier is increased. This increases the amount of fuel needed for melting of the reduced iron to thereby increase energy consumption.
Further, since pressing is performed at high pressures for the purposes of long distance transportation, the roller presses are easily worn. Accordingly, production costs are increased by the rise in equipment expenses.
In addition, in the case where fine direct reduced iron is compacted to a plate or corrugated irregular shape, the compacted material becomes split apart along its length if formation is to at least a predetermined thickness. In this case, since a flattened shape results after the compacted material is made thinner and crushed, when charged in the melter-gasifier, the compacted material is densely packed such that the ventilation in the melter-gasifier is reduced.
Finally, in the case where fine direct reduced iron is roll pressed, it is necessary to increase the amount of fine direct reduced iron that is charged to enhance productivity. This increases the thickness of the compacted material such that it is not continuously formed and instead is interrupted. As a result, the reduction speed of the plate-shaped compacted material is increased such that it passes through a first crusher in a state of not having been crushed. Therefore, much assembled compacted material is produced such that significant stress is given to a second crusher. Further, in the case where the compacted material that is crushed is increased in the second crusher, the amount of powder produced is increased during crushing such that ventilation during charging in the melter-gasifier is deteriorated.